1. Field of the Invention
The present invention relates to an optical module.
2. Related Background of the Invention
There are several kinds of optical modules, such as optical receiver modules, optical transmitter modules, and optical transceiver modules. An optical receiver module includes a light receiving element and converts optical signals into electrical signals. An optical transmitter module includes a light emitting element and converts electrical signals into optical signals. An optical transceiver module includes a receiver assembly and a transmitter assembly. The receiver assembly includes a light receiving element and converts optical signals into electrical signals. The transmitter assembly includes a light emitting element and converts electrical signals into optical signals.
One type of these optical modules includes a metal cover for stabilizing the electrical operation thereof. The present inventors have researched the improvement of the reception sensitivity for the receiver assembly and for the optical receiver module of the above structure. In this research, the present inventors have conducted a variety of experiments to improve the reception sensitivity. As a result, the present inventors have discovered that the electrical charging of the metal cover degrades the reception sensitivity. Therefore, the present inventors have carried out studies on a structure for adding a grounding terminal to the module in order to remove electrostatic charges on the metal cover.
However, there are a number of standards for optical modules that regulate pin assignments, such as the position of a grounding terminal. When developing an optical module that are required to satisfy a standard of these standards, it is not easy to add a grounding terminal to the optical module due to the restriction of the standard. Examples of the standards for optical modules include SFF (Small Form Factor) standard, which relates to optical transceiver modules.
It is, therefore, an object of the present invention to provide an optical module that permits a reduction in the electrical charging of a shielding member.
The optical module according to the present invention comprises an assembly portion and a shielding member. The assembly portion includes an optical device, an electronic element, a circuit board, and a plurality of terminals. The optical device includes a semiconductor optical element. The semiconductor optical element is provided so as to be optically coupled to an optical connector. The electronic element is electrically connected to the semiconductor optical element. The circuit board mounts the electronic element thereon. The plurality of terminals is electrically connected to the circuit board. Further, the shielding member has a reference potential terminal provided so as to be connected to a reference potential line, and shields the assembly portion. In this optical module, the assembly portion has an electrically conductive portion provided so as to connect the shielding member with at least one of the plurality of terminals.
In the optical module, the shielding member is electrically connected to at least one a terminal of the terminals of the assembly portion because the electrically conductive portion of the assembly portion connects the shielding member with at least one of the plurality of terminals.
In the optical module according to the present invention, the assembly portion may include a lead frame member. The lead frame member has an island, first leads, and a second lead. On the island, the circuit board is mounted. The first leads constitute the above-mentioned plurality of terminals, and the second lead constitutes the above-mentioned electrically conductive portion.
The optical module according to the present invention may further comprise an inductive element electrically coupled between the electronic element and the electrically conductive portion. The inductive element reduces the interference of a high frequency component, propagating through the electrically conductive portion, with the electronic element. Further, the inductive element may include a ferrite bead inductor provided on the circuit board.
In the optical module according to the present invention, the circuit board may have a pair of faces and an electrically conductive layer provided on one face of this pair of faces. The electronic element is mounted on the other face of the pair of faces. The island mounts the circuit board thereon through an insulating member.
The insulating member electrically isolates the circuit board from the island, and this island is therefore electrically connected to the circuit board through the inductive element.
The optical module according to the present invention can be provided with the following configurations. The circuit board comprises a pair of edges that extend in a direction of a predetermined axis. The ends of the terminals are arranged along one edge of the pair of edges of the circuit board. The shielding member is provided so as to face the other edge of the pair of edges of the circuit board. The electrically conductive portion is provided so as to extend from one edge of the pair of edges to the other and reaches the shielding member.
In this optical module, the circuit board is provided between the shielding member and the plurality of terminals. The electrically conductive portion is provided so as to extend across a pair of edges of the circuit board. The electrically conductive portion is electrically connected to the shielding member in a region different from the region in which the plurality of terminals are located.
In the optical module according to the present invention, the semiconductor optical element may be a semiconductor light receiving element, and the optical device and the circuit board may be arranged in a direction of a predetermined axis. The electrically conductive portion and the shielding member are connected with each other in a region located in a direction different from the direction in which optical signals propagate.
The optical module according to the present invention may further comprise an additional assembly portion and a housing. The additional assembly portion includes a light emitting device, an additional circuit board, and a plurality of additional terminals. The light emitting device includes a semiconductor light emitting element, and this semiconductor light emitting element is provided so as to be optically coupled to an optical connector. The additional circuit board mounts an additional electronic element electrically connected to the semiconductor light emitting element. The additional circuit board is electrically connected to the additional terminals. The housing includes a holding portion and a receptacle portion. The holding portion holds the assembly portion and the additional assembly portion. The receptacle portion is provided so as to receive the optical connector therein.
The additional circuit board has a pair of edges extending in a direction of a predetermined axis. The ends of the terminals of the additional assembly portion are arranged along one edge of the pair of edges of the additional circuit board. The shielding member is provided so as to face the other edge of the pair of edges of the circuit board. The shielding member shields the additional assembly portion. In the optical module, the assembly portion and the additional assembly portion are capable of implementing the transmission or reception of optical signals and are shielded by the shielding member connected to the electrically conductive portion.
In the optical module according to the present invention, the assembly portion and the additional assembly portion are arranged along a predetermined plane. In this arrangement, the optical module can be provided with a number of assembly portions and an electrically conductive portion that is electrically connected to the shielding member.
The optical module according to the present invention may further comprise a resin member for molding the assembly portion. The end of the electrically conductive portion protrudes from the resin member. According to this optical module, the electrically conductive portion is electrically connected to the shielding member with the electronic element molded by the resin member.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.